Various examples of elastomeric structures, including those used in electrical connectors, are known in the art. The following are representative examples: 1) U.S. Pat. No. 4,538,865 (Wakabayashi, et al) describes the use of press-fit structures to hold an elastomeric member within a second member that limits compression of the elastomeric member; 2) U.S. Pat. No. 4,902,234 (Brodsky, et al) teaches multi-layered elastomeric structures with a force redistribution member, the near incompressible nature of the elastomerics used requiring space to expand laterally during compression; 3) U.S. Pat. No. 5,059,129 (Brodsky, et al) teaches multi-layered elastomeric structures having apertures in the lower layer to limit interaction of pressures between the second layer projections; and 4) U.S. Pat. No. 5,385,477 (Vaynkof, et al) describes buckling of members embedded in an elastomeric member and growth of the elastomeric member when space is provided. The following are further examples: U.S. Pat. No. 3,065,446 (Robb, et al); U.S. Pat. No. 4,647,125 (Landi, et al); U.S. Pat. No. 5,037,312 (Casciotti, et al); U.S. Pat. No. 5,099,393 (Bentlage, et al) and U.S. Pat. No. 5,219,293 (Imamura).
Typically, there are limitations with elastomeric structures such as those described above, including, e.g., the situation in which reducing the hardness of the elastomer by adding foaming agents to the elastomer to increase its compliance in turn increases the material's stress relaxation due to leakage of gases in the foamed elastomer), thereby varying the contact normal force available for a reliable electrical connection. Over-constraining the elastomer or not leaving enough room for it to expand increases the material pressure and, inherently, the resulting contact force due to the incompressible nature of such known elastomeric materials. Another limitation of known elastomeric materials is the possibility of in-plane or lateral growth of such structures due to compression. This in-plane growth can cause positional tolerance and/or alignment problems with other components in a connector system. This growth is caused by an elastomer's Poission's effect, or, in other words, the near incompressibility of homogeneous elastomeric materials, causing expansion in the direction of least work. The in-plane or lateral growth of an elastomeric structure such as the type shown in U.S. Pat. No. 5,059,129 (FIGS. 5 and 6) can cause an additional bending moment in the elastomeric's upstanding projections and first layer. These additional moments are known as column buckling or the "P-delta" effect. As the dimensions "OS" and "PS" in FIG. 7 of U.S. Pat. No. 5,059,129 are reduced or become smaller (e.g., as a result of miniaturization of an electronic package), the cylinder diameter must also become smaller to maintain the most compliant (inverse of spring rate) structure possible. Because of this, the elastic stability of such structures may be reduced, leading to a potential buckling in the structure.
It is one purpose of this invention to teach a means for minimizing the buckling or "P-delta" effect in an elastomeric structure. As an example of how a sparsely connected elastomeric structure can buckle, a single cylinder with no lateral or displacement forces applied (and having a height to diameter aspect ratio of approximately 1.5) can be compressed approximately twenty-five percent of its height without buckling. However, if a similar cylinder is used near the outer edge of a prearranged configuration as shown in FIG. 6 of 5,059,129, with the distance between the cylinders reduced, and the resulting array compressed approximately twenty-five percent, the lateral growth of the array can cause cylinder deformation in a lateral direction, resulting in buckling. This buckling of the cylinder can cause loss of contact normal force, reducing the reliability of the overall contact system.
It is believed that an elastomeric structure capable of overcoming the aforementioned disadvantages associated with known structures would constitute a significant advancement in the art.